Conditioning and writing of multiple gas discharge panel

ABSTRACT

There is disclosed the improved electronic conditioning and addressing of a multiple gas discharge display/memory panel. In the operation of a row-column gas discharge display/memory panel which comprises a discharge cell matrix wherein one or more discharge cells are to-be-addressed along a common row or column and wherein the border of the panel matrix comprises a plurality of pilot cells, the improvement wherein the to-be-addressed cells are electronically conditioned before addressing by applying a conditioning voltage pulse to the common row or column of to-beaddressed cells and wherein a low impedance electrical path is provided between the conditioned row or column of cells and all of the rows or columns of cells orthogonal to the conditioned row or column so as to return the conditioned cells to a neutral state, the magnitude of the conditioning pulse being sufficient to cause discharge of cells in the off-state, but not sufficient to cause discharge of cells in the on-state, and simultaneously applying an addressing voltage to each conditioned to-beaddressed cell immediately after the conditioning voltage pulse without returning the to-be-addressed cell to a neutral state.

United States Patent [1 1 Miller CONDITIONING AND WRITING OF US. Cl. 340/324 M, 315/169 R, 340/166 EL Int. Cl. G08b 5/36 Field of Search 340/324 R, 324 M,

340/166 R, 166 EL; 315/169 R, 169 TV References Cited UNITED STATES PATENTS 3/1970 Baker et a1 315/169 R 1/1971 Bitzer et a1 340/173 PL 6/1971 Hoffetal ..3l5/l69R 11/1971 Johnson 'et al. 340/324 M Primary Examiner-David L. Trafton Attorney-Donald Keith Wedding et a1.

[ ABSTRACT There is disclosed the improved electronic condition- Jan. 15, 1974 ing and addressing of a multiple gas discharge display/memory panel. In the operation of a row-column gas discharge display/memory panel which comprises a discharge cell matrix wherein one or more discharge cells are to-be-addressed along a common row or column and wherein the border of the panel matrix comprises a plurality of pilot cells, the improvement wherein the to-be-addressed cells are electronically conditioned before addressing by applying a conditioning voltage pulse to the common row or column of to-be-addressed cells and wherein a low impedance electrical path is provided between the conditioned row or column of cells and all of the rows or columns of cells orthogonal to the conditioned row or column so as to return the conditioned cells to a neutral state, the magnitude of the conditioning pulse being sufficient to cause discharge of cells in the off-state, but not sufficient to cause discharge of cells in the onstate, and simultaneously applying an addressing voltage to each conditioned to-be-addressed cell immediately after the conditioning voltage pulse without returning the to-be-addressed cell to a neutral state.

4 Claims, 6 Drawing Figures 400F637; View/7' CONDITIONING AND WRITING OF MULTIPLE GAS DISCHARGE PANEL RELATED APPLICATIONS No. 135,021 filed Apr. 19, 1971, now US. Pat. No.

BACKGROUND OF THE' INVENTION This invention relates to the simultaneous conditioning and addressing of multiple gas discharge devices within the same sustaining voltage cycle, especially multiple gas discharge display/memory panels or units which have an electrical memory and which are capable of producing a visual display or representation of data such as numerals, letters, radar displays, aircraft displays, binary words, educational displays, etc.

Multiple gas discharge display and/or memory panels of one particular type with which the present invention is concerned are characterized by an ionable gaseous medium, usually a mixture of at least two gases at an appropriate gas pressure, in a thin gas chamber or space between a pair of opposed dielectric charge storage members which are backed by conductor (electrode) members, the conductor members backing each dielectric member typically being appropriately oriented so as to define a plurality of discrete gas discharge units or cells.

- in some prior art panels the discharge units are additionally defined by surrounding or confining physical glass plates and the like so as to be physically isolated relative to other units. In either case, with or without the confining physical structure, charges (electrons, ions) produced upon ionization of the elemental gas volume of-a selected discharge unit, when proper alternating operating potentials are applied to selected conductors thereof, are collected upon the surfaces of the dielectric at specifically defined locations and constitute an electrical field opposing the electrical field which created them so as to terminate the discharge for 4 the remainder of the half cycle and aid in the initiation of a discharge on a succeeding opposite half cycle of applied voltage, such charges as are stored constituting an electrical memory.

Thus, the dielectric layers prevent the passage of sub stantial conductive surrent from the conductor mem bers to the gaseous medium ane also serve as collecting surfaces for ionized gaseous medium charges (electrons, ions) during the alternate half cycles of the AC. operating potentials, such charges collecting first on one elemental or discrete dielectric surface area and then on an opposing elemental or discrete dielectric surface area on alternate half cycles to constitute an electrical memory.

. An example of a panel structure containing nonphysically isolated or open discharge units is disclosed in U.S. Pat. No. 3,499,167 issued to Theodore C. Baker, et al.

An example of a panel containing physically isolated Proceeding of the Fall Joint Computer Conference, IEEE, San Francisco, Calif., Nov. 1966, pp. 541-547. Also reference is made to U.S. Pat. No. 3,559,190.

In the construction of the panel, a continuous volume of ionizable gas is confined between a pair of dielectric surfaces backed by conductor arrays typically forming matrix elements. The cross conductor arrays may be orthogonally related (but any other configuration of conductor arrays may be used) to define a plurality of opposed pairs of charge storage areas on the surfaces of the dielectric bounding or confining the gas. Thus, for a conductor matrix having H rows and C columns the number of elemental discharge units will be the product H X C and the number of elemental or discrete areas will be twice the number of such elemental discharge units.

In addition, the panel may comprise a so-called monolithic structure in which the conductor arrays are created on a single substrate and wherein two or more arrays are separated from each other and from the gaseous medium by at least one insulating member. In such a device the gas discharge takes place not between two opposing electrodes, but between two contiguous or adjacent electrodes on the same substrate; the gas being confined between the substrate and an outer retaining wall.

It is also feasible to have a gas discharge device wherein some of the conductive or electrode members are in direct contact with the gaseous medium and the In addition to the matrix configuration, the conductor arrays may be shaped otherwise. Accordingly, while structure such as by cells or apertures in perforated 35 the preferred conductor arrangement is of the crossed grid type as discussed herein, it is likewise apparent that where a maximal variety of two dimensional display patterns is not necessary, as where specific standardized visual shapes (e.g., numerals, letters, words, etc.) are to be formed and image resolution is not critical, the conductors may be shaped accordingly, i.e., a segmented display.

The gas is one which produces visible light or invisible radiation which stimulates a phosphor (if visual display is an objective) and a copious supply of charges (ions and electrons) during discharge.

In prior art, a wide variety of gases and gas mixtures have been utilized as the gaseous medium in a gas discharge device. Typical of such gases include C0; C0 halogens; nitrogen; NH oxygen; water vapor; hydro gen; hydrocarbons; P 0 boron fluoride, acid fumes; TiCh; Group VIII gases; air; H 0 vapors of sodium, mercury, thallium, cadmium, rubidium, and cesium; carbon disulfide,laughing gas; H S; deoxygenated air; phosphorus vapors; C l-l CH napthalene vapor; anthracenc; freon; ethyl alcohol; methylene bromide; heavy hydrogen; electron attaching gases; sulfur hexafluoride; tritium; radioactive gases; and the rare or inert gases.

In one preferred embodiment hereof the medium comprises at least one rare gas, more preferably at least two, selected from neon, argon, krypton, xenon, or radon. Likewise, beneficial amounts of helium or mercury may be present.

or discrete dielectric area within the perimeter of such areas, especially in a panel containing non-isolated units. As described in the Baker, et al. patent, the space between the dielectric surfaces occupied by the gas is such as to permit photons generated on discharge in a selected discrete or elemental volume of gas to pass freely through the gas space and strike surface areas of dielectric remote from the selected discrete volumes, such remote, photon struck dielectric surface areas thereby emitting electrons so as to condition at least one elemental volume other thanthe elemental volume in which the photons originated.

With respect to the memory function of a given discharge panel, the allowable distance or spacing between the dielectric surfaces depends, inter alia, on the frequency of the alternating current supply, the distance typically being greater for lower frequencies.

While the prior art does disclose gaseous discharge devices having externally positioned electrodes for initiating a gaseous discharge, sometimes called electrodeless discharge, such prior art devices utilized frequencies and spacings or discharge volumes and operating pressures such that although discharged are initiated in the gaseous medium, such discharges are ineffective or not utilized for charge generation and storage at higher frequencies; although charge storage may be realized at lower frequencies, such charge storage has not been utilized in a display/memory device in the manner of the Bitzer-Slottow or Baker, et al. invention.

The term memory margin is defined herein as M. M. (V VE)/V,/2 where V, is the half amplitude of thesmallest sustaining voltage signal which results in adischarge every half cycle, but at which the cell is not bi-stable and V is the half amplitude of the minimum applied voltage sufficient to sustain discharges once initiated.

It will be understood that the basic electrical phenomenon utilized in this invention is the generation of charges (ions and electrons) alternately storable at pairs of opposed or facing discrete points or areas on a pair of dielectric surfaces backed by conductors connected to a source of operating potential. Such stored charges result in an electrical field opposing the field produced by the applied potential that created them and hence operate to terminate ionization in the elemental gas volume between opposed or facing discrete points or areas of dielectric surface. The term sustain a discharge means producing a sequence of momentary discharges, at least one discharge for each half cycle of applied alternating sustaining voltage, once the elemental gas-volume has been fired, to maintain alternate storing of charges at pairs of opposed discrete areas on the dielectric surfaces.

As used herein, a cell is in the on state when a quantity of charge is stored in the cell such that on each half cycle of the sustaining voltage, a gaseous discharge is produced.

In addition to the sustaining voltage, other voltages may be utilized to operate the panel such as firing and addressing voltages.

A "firing voltage" is any voltage, regardless of source, required to discharge a cell. Such voltage may be completely external in origin or may be comprised of internal cell wall voltage in combination with externally originated voltages.

An addressing voltage is that voltage produced on the panel X Y electrode coordinated such that at the selected cell or cells, the total voltage applied across the cell is equal to or greater than the firing voltage whereby the cell is discharged.

In operation of a multiple gaseous discharge device,

'of the type described hereinbefore, it is necessary to condition the discrete elemental gas volume of each discharge by supplying at least one free electron thereto such that a gaseous discharge can be initiated when the unit is addressed with an operating voltage signal.

The prior art has disclosed and practiced various means for conditioning gaseous discharge units.

One such method comprises the use ofexternal radiation, such as flooding part or all of the gaseous medium of the panel with ultraviolet radiation. This external conditioning method has the obvious disadvantage that it is not always convenient or possible to provide external radiation to a panel, especially if the panel is in a remote position. Likewise, an external UV source requires auxiliary equipment. Accordingly, the use of internal conditioning is generally preferred.

One internal conditioning means comprises using in ternal radiation, such as by the inclusion of a radioactive material and/or by the use of one of more so-called pilot discharge units in the on state for the generation of photons.

As described in the Baker, et al. patent, the space between the dielectric surfaces occupied by the gas is such as to permit photons generated on discharge in a selected discrete or elemental volume of gas (discharge unit) to pass freely through the panel gas space so as to condition other and more remote elemental volumes of other discharge units.

However, such internal photon generation and electron conditioning of the panel gaseous medium becomes unreliable when a given discharge unit to be addressed is remote in distance (an inch or more) relative to the conditioning source, e.g., the pilot unit. Thus, a multiplicity of pilot units or cells may be required for the conditioning of a panel having a large geometric area. In one highly convenient arrangement, the panel border (perimeter) is comprised of a plurality of such pilot cells.

Another means of panel conditioning comprises a socalled electronic process whereby an electronic conditioning signal or pulse is periodically applied to all of the panel discharge units, as disclosed for example in British patent specification 1,161,832, page 8, lines 56 to 76. Reference is also made to U.S. Pat. No. 3,559,190 and The Device Characteristics of the Plasma Display Element by Johnson, et al., IEEE Transactions On Electron Devices, September, 1971. However, electronic conditioning is self-conditioning and is only effective after a discharge unit has been previously conditioned; that is, electronic conditioning involves periodically discharging a unit and is therefore a way of maintaining the presence of free electrons. Accordingly, one cannot wait too long between the periodically applied conditioning pulses since there must be at least one free electron present in order to discharge and condition a unit.

In accordance with the practice of this inveniton, there is provided an improved process of electronically conditioning and addressing multiple gaseous discharge panels, especially panels having a large geometric area.

More particularly, there is provided a process for electronically conditioning and addressing a multiple gas discharge display/memory panel comprising a plurality of gas discharge cells arranged in a row-column matrix wherein one or more discharge cells are to-beaddressed along a common row or column and wherein the border of the panel matrix comprises a plurality of pilot cells, which process comprises applying a conditioning voltage pulse to the common row or column of to-be-addressed cells and simultaneously addressing each conditioned to-be-addressed cell within the same sustaining voltage cycle of the conditioning voltage applied to the cell, and providing a low impedance electrical path between the conditioned row or column of cells and all of the rows or columns of cells orthogonal to the conditioned row or column so as to return the conditioned cells to a neutral state, the magnitude of the conditioning pulse being sufficient to cause discharge of cells in the off-state, but not sufficient to cause discharge of cells in the on-state.

The discharge of the conditioning cells is further effected by having one or more pilot cells in the on state in the panel border at or near the vicinity of the ends of the row or column. Thus, at least the end cells of the row or column are well-conditioned relative to more remote cells in the row, and when they are discharged or fired by the conditioning pulse, they will condition other cells in the row so that every cell of the conditioning row has been well enough conditioned to tire.

The above, as well as other objects, features and advantages of the invention will become apparent and better understood by reference'to the following detailed description when considered inconnection with the accompanying drawings wherein:

FIG. 1 is a partially cut-away plan view of a gaseous discharge display/memory panel as connected to a diagrammatically illustrated source of operating potentials,

FIG. 2 is a cross-sectional view (enlarged, but not to proportional scale since the thickness of the gas volume, dielectric members and conductor arrays have been enlarged for pusposes of illustration) taken on lines 2 2 of FIG. 1,

FIG. 3 is an explanatory partial cross-sectional view similar to FIG. 2 (enlarged, but not to proportional scale) FIG. 4 is an isometric view of a gaseous discharge display/memory panel;

FIG. 5 illustrates a panel matrix comprising X electrodes and Y electrodes;

FIG. 6 is an illustration of the voltages to be applied to the electrodes of FIG. 5.

The invention utilizes a pair of dielectric films of coatings l0 and II separated by a thin layer or volume of a gaseous discharge medium 12, said medium 12 producing a copious supply of charges (ions and electrons) which are alternately collectable on the surfaces of the dielectric members at opposed or facing elemental or discrete areas X and Y defined by the conductor matrix on nongas-contacting sides of the dielectric members, each dielectric member presenting large open surface areas and a plurality of pairs of elemental X and Y areas. While, the electrically operative structural members such as the dielectric members and II and conductor matrixes l3 and 14 are all realtively thin (being exaggerated in thickness in the drawings) they are formed on and supported by rigid nonconductive support members 16 and 17 respectively.

Preferably, one or both of nonconductive support members 16 and I7 pass light produced by discharge in the elemental gas volumes. Preferably, they are transparent glass members and these members essen- 'tially define the overall thickness and strength of the panel. For example, the thickness of gas layer 12 as determined by spacer I5 is under 10 mils and preferably about 5 to 6 mils, dielectric layers 10 and 11 (over the conductors at the elemental or discrete X and Y areas) is between I and 2 mils thick, and conductors l3 and 14 about 8,000 angstroms thick (tin oxide). However, support members 16 and 17 are much thicker (particularly larger panels) so as to provide as much ruggedness as may be desired'to compensate for stresses in the panel. Support members 16 and 17 also serve as heat sinks for heat generated by discharges and thus minimize the effect of temperature on operation of the device. If it is desired that only the memory function be utilized, then none of the members need be transparent to light although for purposes described later herein it is preferred that one of the support members and members formed thereon be transparent to or pass ultraviolet radiation.

Except for being nonconductiveor good insulators the electrical properties of support members 16 and 17 are not critical. The main function of support members 16 and 17 is to provide mechanical support and strength for the entire panel, particularly with respect to pressure differential acting on the panel and thermal shock. As noted earlier, they should have thermal expansion characteristics substantially matching the thermal expansion characteristics of dielectric layers 10 and 11. Ordinary AII'lCh commercial grade soda lime plate glasses have been used for this purpose. Gther glasses such as low expansion glasses or transparent devitrified glasses can be used provided they can withstand processing and have expansion characteristics substantially matching expansion characteristics of the dielectric coatings l0 and 11. For given pressure differentials and thickness of plates, the stress and deflection of plates may be determined by following standard stress and strain formulas (see R. J. Rorak, Formulas for Stress and Strain, McGraw-l-Iill, I954).

Spacer 15 may be made of the same glass material as dielectric films 10 and I1 and may be an integral rib formed on one of the dielectric members and fused to the other members to forma bakeable hermetic seal enclosing and confining the ionizable gas volume 12. However, a separate final hermetic seal may be effected by a high strength devitrified glass sealant 15S. Tubulation 18 is provided for exhausting the space between dielectric members 10 and II and'filling that space with the volume of ionizable gas. For large panels small beadlike solder glass spacers such as shown at 1513 may be located between conductors intersections and fused to dielectric member 10 and 11 to aid in withstanding stress on the panel and maintain uniformity of thickness of gas volume 12.

Conductor arrays 13 and 14 may be formed on support members 16 and 17 by a number of well known processes, such as photoetching, vacuum deposition, stentil screening, etc. In the panel shown in FIG. 4, the center-to-center spacing of conductors in the respective arrays is about 30 mils. Transparent or semitransparent conductive material such as tin oxide, gold or aluminum can be used to form the conductor arrays and should have a resistance less than 3,000 ohms per line. It is important to select a conductor material that is not attacked during processing by the dielectric material.

It will be appreciated that conductor arrays 13 and 14 may be wires of filaments of copper, gold, silver or aluminum or any other conductive metal or material. For example 1 mil wire filaments are commercially available and may be used in the invention. However, formed in situ conductor arrays are preferred since they may be more easily and uniformly placed on and adhered to the support plates 16 and 17.

Dielectric layer members 10 and 11 are formed of an inorganic material and are preferably formed in situ as an adherent film or coating which is not chemically or physically effected during bake-out of the panel. One such material is a solder glass such as Kimble SG-68 manufactured by and commercially available from the assignee of the present invention.

This glass has thermal expansion characteristics substantially matching the thermal expansion characteristics of certain soda-lime glasses, and can be used as the dielectric layer when the support members 16 and 17 are soda-lime glass' plates. Dielectric layers 10 and 11 must be smooth and have a dielectric strength of about 1,000 v. and be electrically homogeneous on a microscopic scale (e.g., no cracks, bubbles, crystals, dirt, surface films, etc.). In addition, the surfaces of dielectric layers 10 and 11 should be good photoemitters of electrons in a baked out condition. However, a supply of free electrons for conditioning gas 12 for the ionization process may be provided by inclusion of a radioactive material within the glass or gas space. A preferred range of thickness of dielectric layers 10 and 11 overlying the conductor arrays 13 and 14 is between 1 and 2 mils. Of course, for an optical display at least one of dielectric layers l and 11 should pass light generated on discharge and be transparent or translucent and, preferebly, both layers are optically transparent.

The preferred spacing between surfaces of the dielectric films is about to 6 mils with conductor arrays 13 and 14 having center-to-center spacing of about 30 mils.

The ends of conductors 14-1 14-4 and support member 17 extend beyond the enclosed gas volume 12 and are exposed for the purpose of making electrical connection to interface and addressing circuitry 19. Likewise, the ends of conductors 13-1 13-4 on support member 16 extend beyond the enclosed gas volume l2 and are exposed for the purpose of making electrical connection to interfaceand addressing circuitry 19.

As in known display systems, the interface and addressing circuitry or system 19 may be relatively inexpensive line scan systems or the somewhat more expensive high speed random access systems. However, it is to be noted that a lower amplitude of operating potentials helps to reduce problems associated with the interface circuitry between the addressing system and the display/memory panel, per se. Thus, providing a panel having greater uniformity in the discharge characteristics throughout the panel, tolerances and operating characteristics of the panel with,which the interfacing circuitry cooperate, are made less rigid.

Although not illustrted in the drawing, a multiplicity of pilot cells are located in the general vicinity of the matrix border conditioning row and/or column in order to facilitate conditioning of the cells therein. Such pilot is continuously in the ON state and is photonically connected to one or more of the cells to be discharged in the selected row or column.

The practice of this invention enables one to more economically operate a gas discharge display/memory panel by applying a conditioning voltage only to the row or column wherein cells are to be addressed, the pulse being of any suitable frequency and waveform (square, sine, triangle, etc.) Likewise, more efficient and higher speed operation is obtained by applying the addressing voltage to the cell within the same sustaining voltage cycle of the conditioning voltage.

The low impedance electrical path between the conditioned row or column of cells and the rows or columns orthogonal thereto may be provided by any convenient electrical circuit means, such as a noninductive switching device as described in copending U.S. Patent application Ser. No. 135,021, filed April 19, 1971 by Donald D. Leuck and assigned to the same assignee as the instant application. Likewise, inductive switching means may be utilized.

Other circuit means are disclosed in U.S. Pat. No. 3,513,327 and copending U.S. Patent applications Ser. No. 60,402, filed Aug. 5, 1970, and Ser. No. 62,015, filed Aug. 7, 1970, both assigned to the same assignee as the instant application.

In FIG. 5 of the drawing there is shown a panel matrix comprising X electrodes and Y electrodes. X and Y are the non-to-be-addressed electrodes whereas X, and Y, are the to-be-addressed electrodes, the intersection of X and Y being the to-be-addressed cell.

In FIG. 6 there is illustrated the voltages to be applied to the X and Y electrodes of FIG. 5 in accordance with this invention.

Thus, in 6(a) there is shown the conditioning pulse applied to Y,. Immediately after the application of this conditioning pulse to Y,,, there is applied a neutralizing pulse in 6(b) to all of the not-to-be-addressed X-axis tral state. The net result of 6(c) and 6(b) is shown by 6(a).

In accordance with this invention an addressing voltage-instead of a neutralizing voltage is applied to the to-be-addressed electrode X, immediately after the conditioning voltage. This is shown by 6(d). The result of 6(c) and 6(d) is shown by 6(e), the net voltage for the cell X,, Y,.

I claim:

1. In a process for operating a multiple gaseous discharge display/memory panel containing an ionizable gaseous medium and having a plurality of discharge cells formed by a series of transversely positioned electrodes, the discharge cells being geometrically arranged in a metrix of rows and columns, and wherein one or more cells are to-be-addressed along a common row or column or cells and wherein the border of the panel matrix comprises a plurality of pilot cells.

the improvement which comprises applying a conditioning voltage pulse to the common row or column of to-be-addressed cells and then providing a low impedance electrical path between the conditioned row or column of cells and all of the rows or columns of cells orthogonal to the conditioned row or column so as to return the conditioned cells to a neutral state, the magnitude of the conditioning pulse being sufficient to cause discharge of cells in the off-state, but not sufficient to cause discharge 3. The invention of claim 1 wherein the gas medium comprises at least two rare gases selected from neon, argon, radon, krypton, and xenon.

4. The invention of claim 3 wherein the gas medium contains beneficial amounts of at least one member selected from helium and mercury. 

1. In a process for operating a multiple gaseous discharge display/memory panel containing an ionizable gaseous medium and having a plurality of discharge cells formed by a series of transversely positioned electrodes, the discharge cells being geometrically arranged in a metrix of rows and columns, and wherein one or more cells are to-be-addressed along a common row or column or cells and wherein the border of the panel matrix comprises a plurality of pilot cells. the improvement which comprises applying a conditioning voltage pulse to the common row or column of to-be-addressed cells and then providing a low impedance electrical path between the conditioned row or column of cells and all of the rows or columns of cells orthogonal to the conditioned row or column so as to return the conditioned cells to a neutral state, the magnitude of the conditioning pulse being sufficient to cause discharge of cells in the off-state, but not sufficient to cause discharge of cells in the on-state, and simultaneously applying an addressing voltage to each conditioned to-beaddressed cell immediately after the conditioning voltage pulse without returning the to-be-addressed cell to a neutral state.
 2. The invention of claim 1 wherein the gaseous medium comprises at least one rare gas.
 3. The invention of claim 1 wherein the gas medium comprises at least two rare gases selected from neon, argon, radon, krypton, and xenon.
 4. The invention of claim 3 wherein the gas medium contains beneficial amounts of at least one member selected from helium and mercury. 